1. Field of the Invention
The present invention relates to an image forming apparatus, more specifically relates to an image forming apparatus configured to calculate a toner consumption based on a totaling result of a pixel value of each pixel of an image formed on a photosensitive member.
2. Description of Related Art
Among copying machines and multi function printers (MFPs) having a copying function using a conventional image forming apparatus, a type capable of measuring a toner consumption is known (for example, see Japanese Patent Application Laid-Open No. 11-84963 (1999) and Japanese Patent Application Laid-Open No. 2002-268484). In such a type of multi function printer, by measuring the toner consumption, it becomes possible to charge in accordance with the toner consumption and perform maintenance based on the toner consumption.
FIG. 1A is a block diagram showing an example of a counter (totaling unit) CP which totals a pixel value of each pixel formed on a photosensitive member, in the multi function printer using the aforementioned conventional image forming apparatus. The counter CP comprises a memory 90 such as a flash memory which stores a cumulative value of a pixel value and an adder 94 which adds image data (pixel value) to the cumulative value stored in the memory 90. The cumulative value of the pixel value stored in the memory 90 is almost proportional to the toner consumption. Accordingly, the toner consumption can be calculated based on the cumulative value stored in the memory 90.
FIG. 1B is a schematic view showing a relation between the image data (pixel value) and the cumulative value in the multi function printer using the aforementioned conventional image forming apparatus. It is shown that a state in which the image data (pixel value) is added to the cumulative value of the memory 90 by the adder 94. Note that “n” of the cumulative value in FIG. 1B is an integer representing the cumulative value before starting a density totaling processing of sequentially adding each image data (pixel value) shown in FIG. 1B to the cumulative value, that is, before adding the image data (pixel value) “255” to the cumulative value.
However, among the copying machines and the multi function printers using the conventional image forming apparatus having the copying function, there is also the case where not only an original image such as a read image, a print image, a FAX received image, and the like formed with a user's intention of image forming, but also the image formed without the user's intention of image forming, is formed on the photosensitive member. As examples of the image formed without the user's intention of image forming, there are an adjustment image for adjusting a density or forming position of the image formed on the photosensitive member but not transferred to a sheet, and a composing image (an image to be composed with another image) such as a forgery preventing image or an identifying image which is composed with an original image, to prevent forgery or specify a printer. Therefore, conventionally, there is also the case where totaled pixel values include the pixel value of the image formed without the user's intention of image forming.
In such case, for example, it becomes necessary for the user to pay a charge of a toner, even for the toner used in forming the adjustment image. Accordingly, when all of replenished toner is consumed in a period of time shorter than a supposed period of time, there may be an inquiry from the user such as “Is there any fault in an apparatus?”. However, it is difficult for a service person to judge a cause whether or not the toner is consumed by actually copying and printing with the user's intention of image forming, whether or not the toner is consumed by a plurality of images formed without the user's intention of image forming, or whether or not the toner consumption is increased by a certain abnormality (for example, the image is developed at a density higher than an ordinary density). Therefore, it has been difficult to investigate the cause of toner consumption in a short period of time as a result.